As is known, urea is produced industrially using processes whereby carbon dioxide reacts with ammonia to form ammonium carbamate, which decomposes into urea and water.
A typical reactor therefore contains a gaseous phase and a liquid phase flowing in co-current flows inside a pressurized reaction chamber.
Conversion of ammonia and carbon dioxide to ammonium carbonate and ultimately urea is enhanced (i.e., to increase urea output) using tray reactors.
Urea tray reactors substantially comprise a normally cylindrical shell, which extends substantially along a normally vertical axis, and is fitted inside with elements (i.e., trays) defined by respective metal sections shaped and/or perforated to divide the reaction chamber into compartments and form specific paths for the substances inside the reactor.
Certain known trays are perpendicular to the vertical axis of the reactor, and equally spaced along the axis to the full height of the reactor.
The trays are very often perforated (i.e., have holes variously arranged and possibly of different shapes and/or sizes).
In one embodiment, the trays are configured to be inserted through the manhole reactors are normally provided with, so they can also be fitted to existing reactors and/or removed and replaced. For which reason, the trays are normally made in a number or quantity of parts that fit together.
The trays have various functions, and in particular:                maximize the hold time of the light (faster) phase;        distribute the reactants as evenly as possible along the reactor section, to prevent ‘back-mixing’;        enhance mixing of the gaseous and liquid phases; and        reduce ‘bubble size’ to improve diffusion of the ammonia in the carbon dioxide.        
Numerous urea reactor tray designs and configurations are known.
Urea reactors with perforated trays are described, for example, in European Patent No. 495418, European Patent No. 781164, U.S. Pat. No. 6,444,180 and U.S. Pat. No. 6,165,315.
Other tray designs for other applications are described in U.S. Pat. No. 3,070,360 and U.S. Pat. No. 3,222,040.
Certain known configurations—particularly those in certain of these patent documents specifically configured for producing urea—indeed provide for increasing output by reducing back-mixing and load losses, by ensuring substantially even distribution of the light (gaseous) and heavy (liquid) phases by providing preferential paths for each of the two phases, and by enabling non-intrusive (non-impact) mixing between one tray and another.
Certain known solutions, however, still leave room for improvement.
Generally speaking, certain known solutions fail to provide for thorough mixing of the light and heavy phases (both including supercritical fluids), which, because of the difference in density, tend to flow along separate preferential paths defined by the configuration and arrangement of the trays, and in particular by the shape, location, and size of the holes in the trays.
This drawback also impairs final conversion of the reactants, thus reducing urea output.